Fold the arcs A B and B C round the arcs B D E, B F E, and make
the sides A G and C H coincide every where together upwards from the point E,
which will represent a cone cut obliquely to
its base, and shew the section to be an ellipsis.
I. Form the whole part of the cone A C B, by bringing the points
A and B together, and bending it so as to become round as near as may be.
II. Bend regularly the other part of the figure, so that the arcs D E, F E,
may surround the arcs F G, F H.
III. Raise up the parabola G I H, making the
point I meet the coincident points A and B; thus may you see the section made
by cutting a cone parallel to one of its sides.
The last directions
(Plate XLI) obtain here; for bringing E and F together, and rounding the part
E D E, as was there described, and the points A and B being brought to G and
H, if the hyperbola G I H be then raised up,
as before directed, the section of a cone, cut parallel to its axis, will be
thereby presented to view.